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Author name code: strous
ADS astronomy entries on 2022-09-14
author:"Strous, Louis H."
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Title: The Formation of a Prominence in Active Region NOAA
8668. I. SOHO/MDI Observations of Magnetic Field Evolution
Authors: Chae, Jongchul; Wang, Haimin; Qiu, Jiong; Goode, Philip R.;
Strous, Louis; Yun, H. S.
2001ApJ...560..476C Altcode:
We have studied the evolution of the photospheric magnetic field in
active region NOAA 8668 for 3 days while the formation of a reverse
S-shaped filament proceeded. From a set of full-disk line-of-sight
magnetograms taken by the Michelson Doppler Imager (MDI) on board
the Solar and Heliospheric Observatory (SOHO), we have found a
large canceling magnetic feature that was closely associated with
the formation of the filament. The positive flux of the magnetic
feature was initially 1.5×10<SUP>21</SUP> Mx and exponentially
decreased with an e-folding time of 28 hr throughout the period of
observations. We also have determined the transverse velocities of
the magnetic flux concentrations in the active region by applying
local correlation tracking. As a result, a persistent pattern of shear
motion was identified in the neighborhood of the filament. The shear
motion had a speed of 0.2-0.5 km s<SUP>-1</SUP> and fed negative
magnetic helicity of -3×10<SUP>42</SUP> Mx<SUP>2</SUP> into the
coronal volume during an observing run of 50 hr at an average rate
of -6×10<SUP>40</SUP> Mx<SUP>2</SUP> hr<SUP>-1</SUP>. This rate is
an order of magnitude higher than the rate of helicity change due to
the solar differential rotation. The magnetic flux of the field lines
created by magnetic reconnection and the magnetic helicity generated
by the photospheric shear motion are much more than enough for the
formation of the filament. Based on this result, we conjecture that the
filament formation may be the visible manifestation of the creation
of a much bigger magnetic structure that may consist of a flux rope
and an overlying sheared arcade.
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Title: Bias in velocity determinations from full-disk solar
observations
Authors: Strous, L. H.
2000SoPh..195..219S Altcode:
Estimates for the global solar surface velocity field can be
obtained from time series of full-disk solar images. However, bias
is introduced by mistakes in the assumptions about the geometry of
the observations, and by imperfections in the optical system. I
investigate many sources of bias and determine their first-order
influence on the measured velocity field (both the transverse and
longitudinal components). Results are presented in analytical and
pictorial form. By comparing bias velocities of unknown origin with
the results, one may obtain clues to the cause of the bias.
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Title: The Dynamics of the Excitation of Solar Oscillations
Authors: Strous, Louis H.; Goode, Philip R.; Rimmele, Thomas R.
2000ApJ...535.1000S Altcode:
We investigate seismic events, bursts of seismic waves that are
generated locally just below the solar surface and that we detect
traveling up through the photosphere. We identify a few thousand
seismic events by their traveling wave character and find that they
are associated with continuum darkening and downflow and have an
extent of on average about 10-15 minutes and 1 Mm. Their birth rate
is about 8×10<SUP>-16</SUP> m<SUP>-2</SUP> s<SUP> -1</SUP>. The
observed upwardly traveling seismic flux in the average event
(as derived from velocities in the p-mode region of k-ω space) is
followed after about 3 minutes by some reflected downward flux. Only
a small fraction of the energy generated in the hypocenter of the
event below the surface travels straight up for us to see. The bulk
of the generated energy is directed or reflected downward, and is
eventually transformed into p-modes. The seismic events at the surface
contain about 1.5×10<SUP>19</SUP> J of seismic energy each, which
corresponds to an average flux level of about 8.5 kW m<SUP>-2</SUP>
over the whole surface. The total energy flow is likely more than an
order of magnitude greater, and is then in the same ballpark as the
estimate of Libbrecht for the power required to sustain the p-mode
spectrum. We find a roughly linear relation between the peak seismic
flux and the peak downward convective velocity associated with each
seismic event, which does not fit the highly nonlinear relations found
theoretically by Lighthill and Goldreich & Kumar for stochastic
excitation by turbulent convection, but does fit the monopole source
deduced by Nigam & Kosovichev from a study of the p-mode spectrum.
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Title: Large-Scale Surface Flow Patterns on the Sun
Authors: Strous, L. H.
2000SPD....31.0104S Altcode: 2000BAAS...32..801S
I derive the large-scale flow field at the solar surface from tracking
features at supergranular scale (10 Mm) through SOHO/MDI full-disk
Dopplergrams recorded during 62 days in 1996 and reduced at Stanford
University to a dataset with a pixel scale of 1.39 Mm and a cadence of
15 minutes. Both the dataset and the reduction algorithms are improved
compared to earlier investigations. I present measurements, derived from
supergranular motion, of differential rotation and meridional flow, and
synoptic maps of the solar surface flow and its variation in time. This
work is supported by the SOI/MDI project at Stanford University and
Lockheed Martin Solar & Astrophysics Laboratory (grant NAG5-3077).
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Title: De veranderlijke zon.
Authors: Strous, L.
2000Zenit..27..148S Altcode:
No abstract at ADS
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Title: Phenomena in an Emerging Active Region. II. Properties of
the Dynamic Small-Scale Structure
Authors: Strous, Louis H.; Zwaan, Cornelis
1999ApJ...527..435S Altcode:
The magnetic flux emergence in growing active region NOAA 5617,
when it is about 8 hr old, shows an intricate fine structure. The
small-scale emergence events are characterized by a coincident
upflow and transient darkening (of about 2 Mm and 10 minutes) in the
continuum and line-center intensity followed by the appearance of one,
or in some cases two, new bright grains flanking the line-center
darkening. The bright grains (faculae) coincide with magnetic
flux concentrations and downflows. The footpoints move apart at on
average 1.4 km s<SUP>-1</SUP>. Flux emergence happens recurrently in
a number of locations widely distributed over the active region, which
appear to form a pattern with a wavelength of about 8 Mm. A preferred
orientation that fits Hale's polarity law is displayed by the spatial
pattern in the emergence locations, the emergence events themselves,
subsequent footpoint motion, and the Hα arch filament system. We find
long (~15 Mm) alignments of unipolar faculae of each magnetic polarity
that also follow the preferred orientation. We adapt the model for flux
emergence to accommodate the observed dynamic fine structure. Essential
new features are (1) the emerging bundle of flux tubes is frayed in
two systems, in vertical stacks, arranged in slightly curved, nearly
parallel sheets; and (2) many flux tubes emerge in multiple locations.
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Title: Solar Differential Rotation Derived from H-alpha Full Disk
Images by Means of Local Correlation Tracking
Authors: Woodard, M. F.; Denker, C.; Strous, L. H.; BBSO Collaboration;
LMSAL Collaboration
1999AAS...19410007W Altcode: 1999BAAS...31..997W
We present the application of Local Correlation Tracking (LCT)
techniques to time series of contrast-enhanced H-alpha full disk images
taken as part of the synoptic observing program at Big Bear Solar
Observatory (BBS0) during the summer of 1998. A typical set of daily
H-alpha full disk images consists of 600 to 800 individual frames,
taken 30 to 60 s apart, with a 2k x 2k pixel Kodak 4.2 MegaPlus CCD
camera at BBSO's Singer telescope. For each pair of successive images,
we compute displacement vectors over a 64 x 64 element cartesian
grid covering the solar disk. The resulting daily-averaged flow maps
show predominantly solar differential rotation and proper motions in
active regions. We remap the flow maps to heliographic coordinates and
determine a Legendre polynomial expansion of the daily differential
rotation profile. We present preliminary findings regarding differential
rotation based on different types of features seen in H-alpha, such as
quiet-sun fibrils, plages, and dark filaments. We discuss the relation
of our differential rotation profiles to profiles derived by other
methods and address the question of time variability. The work at
BBSO is supported by ONR under grant N00014-97-1-1037, by NSF under
grant ATM 97-14796, and by NASA under grant NAG 5-4919. Louis Strous
is supported by NASA NAG5-3077 to Stanford University.
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Title: Average Properties of Flux Emergence in Young Active Region
5617
Authors: Strous, L.
1999ASPC..183..551S Altcode: 1999hrsp.conf..551S
No abstract at ADS
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Title: Properties of Small-Scale Flux Emergence in a Young Active
Region
Authors: Strous, Louis; Zwaan, Cornelis
1999soho....9E..82S Altcode:
The magnetic flux emergence in growing active region NOAA 5617, when
it is about 8 hours old, shows an intricate fine structure. The
small-scale emergence events are characterized by a coincident
upflow and transient darkening (of about 2 Mm and 10 minutes) in the
continuum and line-center intensity, followed by the appearance of
one, or in some cases two, new bright grains flanking the line-center
darkening. The bright grains (faculae) coincide with magnetic flux
concentrations and downflows. The footpoints move apart at on average
1.4 km/s. Flux emergence happens recurrently in a number of locations
widely distributed over the active region, which appear to form
a pattern with a wavelength of about 8 Mm. A preferred orientation
which fits Hale's polarity law is displayed by the spatial pattern in
the emergence locations, the emergence events themselves, subsequent
footpoint motion, and the H-alpha arch filament system. We find long
(~ 15 Mm) alignments of unipolar faculae of each magnetic polarity
that also follow the preferred orientation. We adapt the model for flux
emergence to accommodate the observed dynamic fine structure. Essential
new features are: (1) the emerging bundle of flux tubes is frayed in
two systems; in vertical stacks, arranged in slightly curved, nearly
parallel sheets, and (2) many flux tubes emerge in multiple locations.
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Title: The Excitation of Solar Oscillations -- Observations and
Simulations
Authors: Goode, P.; Strous, L.; Rimmele, T.; Stein, R.; Nordlund, Å.
1999ASPC..183..456G Altcode: 1999hrsp.conf..456G
No abstract at ADS
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Title: The Excitation of Solar Oscillations
Authors: Strous, Louis H.; Goode, Philip R.; Rimmele, Thomas R.
1999soho....9E..81S Altcode:
We investigate seismic events, bursts of seismic waves that are
generated locally just below the solar surface and that we detect
travelling up through the photosphere. We identify 646 seismic events,
which are associated with intergranular lanes and have an extent
of on average about 10 minutes and 3 Mm. Their birth rate is about
10-16 m-2 s-1. The observed upwardly travelling seismic flux in the
average event (as derived from velocities in the p-mode region of
k-omega space) is followed after about 5 minutes by some reflected
downward flux. Only some of the energy generated in the hypocenter of
the event below the surface travels up for us to see. We propose that
this energy is converted into surface (f-mode-like) waves, while the
unseen, initially downward going energy is eventually transformed
into p-modes. The seismic events at the surface contain about 5 *
1019 J of seismic energy each, which corresponds to an average
flux level of about 4 kW/m2 over the whole surface. The initially
downward directed energy flow is likely substantially greater, and
is then in the same ballpark as the estimate of Libbrecht (1988) for
the power required to sustain the p-mode spectrum. We find a roughly
linear relation between the peak seismic flux and the peak downward
convective velocity associated with each seismic event, which is
not equal to the v8 relation found theoretically by Lighthill (1952)
for stochastic excitation by turbulent convection.
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Title: On the Origin of Solar Oscillations
Authors: Goode, Philip R.; Strous, Louis H.; Rimmele, Thomas R.;
Stebbins, Robin T.
1998ApJ...495L..27G Altcode: 1998astro.ph..1008G
We have made high-resolution observations of the Sun in which we
identify individual sunquakes and see power from these seismic events
being pumped into the resonant modes of vibration of the Sun. A typical
event lasts about 5 minutes. We report the physical properties of
the events and relate them to theories of the excitation of solar
oscillations. We also discuss the local seismic potential of these
events.
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Title: 62 Days Around the Sun: A Search for Supergranular Evolution
and Giant Cells
Authors: Strous, Louis H.; Simon, George W.
1998ASPC..140..161S Altcode: 1998ssp..conf..161S
No abstract at ADS
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Title: Supergranular Evolution, Solar Rotation, and a Search for
Giant Cells, using Full-disk SOHO/SOI/MDI Dopplergrams
Authors: Simon, George W.; Strous, Louis H.
1997AAS...19112002S Altcode: 1997BAAS...29.1402S
SOHO/SOI/MDI obtained full-disk dopplergrams of the Sun once per minute
for 62 days from 1996 May 23 to 1996 July 23. From hourly averages
of these dopplergrams we have studied the evolution of supergranules,
measured solar rotation up to high latitudes, and searched for giant
cells.
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Title: Photospheric Differential Rotation from Full-Disk SOI/MDI
Dopplergrams
Authors: Bogart, R. S.; Bai, T.; Scherrer, P. H.; Strous, L. H.;
Simon, G. W.; Tarbell, T. D.
1997SPD....28.0258B Altcode: 1997BAAS...29..903B
We report on measurements of the solar surface differential rotation
made from SOI/MDI full-disk Dopplergrams obtained once per minute during
the 2-month Dynamics Program from 23 May through 26 July 1996. We infer
the rotation profile both from the direct photospheric Doppler signal
and also by tracking Doppler features (supergranules) across the solar
disk. We study the rotation curve as a function of latitude, feature
size, and tracking method, and look for global scale flows. This work
was supported by NASA Grant NAG5-3077 at Stanford and Lockheed Martin,
and by AFOSR and the Fellows Program of AF Phillips Lab at NSO/SP.
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Title: Comparison of Granulation Correlation Tracking (CT) and
Feature Tracking (FT) Results from SOHO/MDI and the Swedish Vacuum
Solar Telescope on La Palma
Authors: Shine, R.; Strous, L.; Simon, G.; Berger, T.; Hurlburt, N.;
Tarbell, T.; Title, A.; Scharmer, G.
1997SPD....28.0262S Altcode: 1997BAAS...29Q.904S
We have computed photospheric velocity flow maps from simultaneous
observations taken with MDI and at the Swedish Vacuum Solar Tower
(SVST) on La Palma on August 15, 1996. Both sets consist of a series
of photospheric images, and flow maps are computed by following the
local motions of granules. The MDI data have the important advantages
of very stable images and longer continuous coverage of the same area
of the solar surface. This longer coverage is necessary to study the
evolution of mesogranules, supergranules, and to detect possible low
amplitude motions on scales larger than supergranules. However, the
high resolution mode of MDI is limited by the small telescope size to
about 1.2 arc seconds angular resolution and uses a 0.6 arc second pixel
size. This is adequate to show granulation but has the rms constrast
significantly reduced to about 2%. Early efforts adapting techniques
that were successful with higher resolution ground based images gave
poor results and although new methods have now been developed, there
are still some problems with accuracy. On the other hand, the SVST
images have much higher angular resolution (as good as 0.2 arc second)
but suffer from variable atmospheric distortion. They also have a much
smaller field of view. By detailed comparison of the two data sets
and by using CT and FT techniques to track the motions, we hope to
understand the sources of any differences between them and to develop
credible correction parameters to the MDI data sets if necessary. This
work was supported by NASA Grant NAG5-3077 at Stanford and Lockheed
Martin, by AFOSR and the Fellows Program of AF Phillips Lab at NSO/SP,
and by the Swedish Royal Academy of Sciences.
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Title: Preliminary SoHO/MDI Observations of Supergranular Evolution
Authors: Simon, G. W.; Strous, L. H.; Matt, S.; Title, A. M.;
Schrijver, C. J.
1997SPD....28.0264S Altcode: 1997BAAS...29R.904S
We present preliminary results of a study into the evolution of
supergranules, using data from SoHO/MDI. We discuss the supergranular
size spectrum, lifetimes, and topological evolution. We compare
structures of supergranular size visible in high-resolution SoHO/MDI
dopplergrams and in divergence maps derived from tracking of features
in dopplergrams. This work was supported by NASA Grant NAG5-3077 at
Stanford and Lockheed Martin, and by AFOSR and the Fellows Program of
AF Phillips Lab at NSO/SP.
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Title: Horizontal Velocity Structure of Supergranules near Disk
Center from High-Resolution SoHO/MDI Observations
Authors: Strous, L. H.; Simon, G. W.; Shine, R. A.; Hurlburt, N.
1997SPD....28.0265S Altcode: 1997BAAS...29S.904S
We determine the average surface flows in supergranules from
high-resolution SoHO/MDI observations near disk center, using local
correlation and feature tracking methods. We present results as a
function of distance to the supergranule center and of supergranule
size, and as a function of normalized distance to the supergranule
center. This work was supported by NASA Grant NAG5-3077 at Stanford and
Lockheed Martin, and by AFOSR and the Fellows Program of AF Phillips
Lab at NSO/SP.
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Title: Comparison of supergranular flows from doppler and local
correlation tracking velocities
Authors: Frank, Z.; Hurlburt, N.; Shine, R.; Tarbell, T.; Simon, G.;
Strous, L.; Matt, S.
1997SPD....28.0259F Altcode: 1997BAAS...29..903F
Measurements of the flows in the solar photosphere rely upon two
techniques: doppler measurements of the line-of-sight velocity
or tracking of features or patterns moving perpendicular to the
line-of-sight. These methods have differing characteristics. Doppler
measurements can easily measure surface flows near the limb
which are not seriously contaminated by p-modes or other solar
sources. However, they require excellent instrument calibration over
the full field of view. Even then vertical flows within supergranules
are barely detectable. Correlation and feature tracking have proven
useful for estimating transverse velocity using granules and other
tracers. Nevertheless, they can be degraded by the intensity variations
of p-modes and possibly other oscillatory motions, as well as by effects
of limb darkening and foreshortening. The two methods would both be
strengthened through detailed comparisons. Data collected by MDI/SOHO is
ideal for this purpose. The data is co-spatial and co-temporal, and is
all obtained through the same instrument. We compare Doppler velocities
with those obtained through correlation tracking using high-resolution
MDI/SOHO images. We focus on motions at positions exceeding 30 degrees
from disk center. After taking projection effects into account, we
combine the two measurements to form a three-dimensional picture of
the flows in the average supergranule. This work was supported by NASA
Grant NAG5-3077 at Stanford and Lockheed Martin, and by AFOSR and the
Fellows Program of AF Phillips Lab at NSO/SP.
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Title: Dynamics of the Chromospheric Network: Mobility, Dispersal,
and Diffusion Coefficients
Authors: Schrijver, Carolus J.; Shine, Richard A.; Hagenaar, Hermance
J.; Hurlburt, Neal E.; Title, Alan M.; Strous, Louis H.; Jefferies,
Stuart M.; Jones, Andrew R.; Harvey, John W.; Duvall, Thomas L., Jr.
1996ApJ...468..921S Altcode:
Understanding the physics behind the dispersal of photo spheric magnetic
flux is crucial to studies of magnetoconvection, dynamos, and stellar
atmospheric activity. The rate of flux dispersal is often quantified by
a diffusion coefficient, D. Published values of D differ by more than a
factor of 2, which is more than the uncertainties allow. We propose that
the discrepancies between the published values for D are the result of
a correlation between the mobility and flux content of concentrations of
magnetic flux. This conclusion is based on measurements of displacement
velocities of Ca II K mottles using an uninterrupted 2 day sequence
of filtergrams obtained at the South Pole near cycle minimum. We
transform the Ca II K intensity to an equivalent magnetic flux density
through a power-law relationship defined by a comparison with a nearly
simultaneously observed magnetogram. One result is that, wherever the
network is clearly defined in the filtergrams, the displacement vectors
of the mottles are preferentially aligned with the network, suggesting
that network-aligned motions are more important to field dispersal than
deformation of the network pattern by cell evolution. The rms value
of the inferred velocities, R = <|v|<SUP>2</SUP>><SUP>½</SUP>,
decreases with increasing flux, Φ, contained in the mottles, from R
≍ 240 m s<SUP>-1</SUP> down to 140 s<SUP>-1</SUP>. The value of R(Φ)
appears to be independent of the flux surrounding the concentration,
to the extreme that it does not matter whether the concentration is
in a plage or in the network. The determination of a proper effective
diffusion coefficient requires that the function R(Φ) be weighted
by the number density n(Φ) of mottles that contain a total flux. We
find that n(Φ) decreases exponentially with Φ and propose a model
of continual random splitting and merging of concentrations of flux to
explain this dependence. Traditional methods used to measure D tend to
be biased toward the larger, more sluggish flux concentrations. Such
methods neglect or underestimate the significant effects of the
relatively large number of the more mobile, smaller concentrations. We
argue that the effective diffusion coefficient for the dispersal of
photo spheric magnetic flux is ∼600 km<SUP>2</SUP> s<SUP>-1</SUP>.
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Title: Observation of the excitation of solar oscillations
Authors: Goode, Philip R.; Strous, Louis H.
1996BASI...24..223G Altcode:
No abstract at ADS
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Title: Preliminary SOI/MDI Observations of Surface Flows by
Correlation Tracking in the Quiet Solar Photosphere and an Emerging
Active Region
Authors: Tarbell, T.; Frank, Z.; Hurlburt, N.; Saba, J.; Schrijver,
C.; Shine, R.; Title, A.; Simon, G.; Strous, L.
1996AAS...188.6914T Altcode: 1996BAAS...28..937T
The extended observation of the solar surface with frequent sampling
provided by MDI on SoHO offers the chance to observe the evolution of
supergranules and to measure surface flows associated with active
regions and perhaps larger scale zonal and meridonal flows. We
have used local correlation tracking of the granulation pattern for
measuring surface flows from MDI high resolution continuum images. The
datasets consist of 1024 x 1024 pixel images collected with a cadence
of one minute and extending many hours each. The images are typically
centered upon the central meridian of the sun and offset to the north
of sun center, spanning roughly 40 degrees of solar longitude and from
approximately -10 to +30 degrees of solar latitude. The latitude
dependence of the differential rotation is evident. We present
preliminary results of our search for signatures of mesogranules,
supergranules and giant cells. On 23 Feb. 1996, we obtained a 12-hour
continuous sequence including quiet sun near disk center and NOAA
region 7946 at about N08 E30. The active region grew rapidly over this
interval, forming several sunpots. We show preliminary comparisons of
the measured flow fields with coaligned SOI/MDI magnetograms taken
at 15-minute intervals. The SOI/MDI program is supported by NASA
grant NAG5-3077.
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Title: Phenomena in an emerging active region. I. Horizontal dynamics.
Authors: Strous, L. H.; Scharmer, G.; Tarbell, T. D.; Title, A. M.;
Zwaan, C.
1996A&A...306..947S Altcode:
Horizontal dynamics in observations of NOAA AR 5617 are studied by
tracking individual elements through the field of view. Small magnetic
elements of both magnetic polarities occur everywhere in the active
region, and define unipolar thread-like concentrations of magnetic
field of up to 15Mm length. The horizontal granular flow field in
the active region is divergent (e-time scale 2.1hours) and clockwise
(time scale 32hours). Facular elements are tracers of (clumps of)
fluxtubes. A hierarchy of movement of magnetic elements appears:
Facular elements everywhere in the active region move obliquely toward
the edges of the active region of the same polarity as their own, faster
than those edges (as defined by strings of pores) move apart. The pores
move along the edges toward the major sunspots of their own polarity,
and the major sunspots of either polarity move apart. The separation
velocity of both polarities of facular elements is about 0.84km/s, of
pores about 0.73km/s, and that of the major sunspots is about 0.50km/s.
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Title: Dark Lanes in Granulation and the Excitation of Solar
Oscillations
Authors: Rimmele, T. R.; Goode, P. R.; Strous, L. H.; Stebbins, R. T.
1995ESASP.376b.329R Altcode: 1995help.confP.329R; 1995soho....2..329R
No abstract at ADS
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Title: Warning: Local Correlation Tracking may BE Dangerous to your
(scientific) Health
Authors: Simon, G. W.; Brandt, P. N.; November, L. J.; Shine, R. A.;
Strous, L. H.
1995ESASP.376b.223S Altcode: 1995soho....2..223S; 1995help.confP.223S
No abstract at ADS
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Title: Feature Tracking: Deriving Horizontal Motion and More
Authors: Strous, L. H.
1995ESASP.376b.213S Altcode: 1995help.confP.213S; 1995soho....2..213S
No abstract at ADS
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Title: Comparison of Flow Maps Derived by Various Techniques
Authors: Strous, L. H.
1995ESASP.376b.219S Altcode: 1995help.confP.219S; 1995soho....2..219S
No abstract at ADS
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Title: Dynamics in Solar Active Regions: Patterns in Magnetic-Flux
Emergence
Authors: Strous, L. H.
1994PhDT.......347S Altcode:
No abstract at ADS
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Title: Dynamics of small magnetic elements in a growing active region
Authors: Strous, L. H.
1994ASIC..433...73S Altcode:
No abstract at ADS
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Title: Predictions of infrared recombination lines in stellar winds
of hot stars
Authors: Strous, L. H.; Lamers, H. J. G. L. M.
1989ESASP.290..385S Altcode: 1989isa..book..385S
Infrared recombination lines can provide accurate estimates
for the velocity and density structure of stellar winds and
thus of mass loss. The authors use a simple stellar wind model,
hydrogenic approximations and scaling laws to derive information about
recombination lines in the ISO range (1 - 100 μm). They estimate that,
for a 40000K star, the boundary-level from above which recombination
lines originate is in the range n = 2 - 10 for the most abundant
elements. The authors give a simple formula to estimate the population
of levels above the boundary-level and use this to produce a table
of predictions of fluxes and equivalent widths of recombination lines
for H, He, C III-IV, N III-V and O III-V.